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Increasing winter chilling in the desert Southwest, 2013-14

Posted by fruitnut z7b-8a,4500ft SW TX (My Page) on
Sat, Feb 1, 14 at 15:17

Thought I might relay my experience at gaining adequate winter chilling in a greenhouse in Alpine, Texas. Winters average about 60/30F day/night temperatures with 75% sunshine.

My plan has been shade over the plants, heat at night, and use evaporative cooling by day. The objective being to maximize Utah chill hrs. That model predicts optimum chilling at 41F, none below 32F or above 59F, and negative chilling above 64F. So Alpine suffers in chilling by being too cold at night and too warm by day.

For 2013-14, I heated to 39-41F, on cold nights the heater comes on at 39 and off at 41. Cooling started stage one at 43F and evaporative cooling at 47F.

For the period Nov 22 thru Jan 30, 69 days, Utah hrs in the greenhouse were 1270, 77% of the total of 1656 hrs. Outside the same period experienced 350 Utah hrs and 751 hrs below 45F.

There are many ways this could be adapted outside a greenhouse. My first year here I used evaporative cooling in winter on potted trees setting in an unheated garage. This was mostly to delay bloom but could be used to increase chilling.

Another setup could be just shade cloth or shade with misting.

This post was edited by fruitnut on Sat, Feb 1, 14 at 15:29


Follow-Up Postings:

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RE: Increasing winter chilling in the desert Southwest, 2013-14

  • Posted by mrclint z10SoCal Valley (My Page) on
    Sat, Feb 1, 14 at 22:16

Fruitnut, have you had fruitset problems due to not enough chill in the past? Or are you seeing greater quality with higher chill?

I'm not one to push the envelope for a particular cultivar, especially in the June-August time frame because almost everything is very good at that time. Now if someone had a dead spot in their successive ripening window, I could see some sort of extra measures being necessary.

The question would be, is the gain worth the effort?


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RE: Increasing winter chilling in the desert Southwest, 2013-14

  • Posted by fruitnut z7b-8a,4500ft SW TX (My Page) on
    Sat, Feb 1, 14 at 22:33

Lack of chilling can affect fruit eating quality. I've read about it especially in peaches. But mainly I've experienced flower bud abortion especially in apricot and to a lesser extent pluots. In cherries the issue has been deformed and infertile flowers resulting in little or no fruit set.

It's worth the effort if I can reliably grow more fruits like the Orangered apricots I had last year. In 2012 fruit set was near zero with that cultivar. In 2013 maybe 5-10% set. We'll see what I get this year.

Besides some of us just like to experiment more than others. It can be a good way to learn even if the fruit isn't better.


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RE: Increasing winter chilling in the desert Southwest, 2013-14

  • Posted by mrclint z10SoCal Valley (My Page) on
    Sun, Feb 2, 14 at 14:46

It's an interesting topic.

I'm putting warm water in my EarthBoxes right now to keep the temps up for tomatoes and zucchini. It's hard to say if it helps or to what degree, but I am harvesting both through Winter. Conversely, would dumping ice (or ice packs) around the drip line in combination with shading make a difference? Surely a small scale effort. My most marginal chill tree would be Royal apricot.

There is some data on icing fruit trees, for fruitset and/or to delay the bloom time.


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